Microelectromechanical systems (MEMS) integrate electrical and mechanical components on a single substrate, such as silicon, using microfabrication technologies. Typically, the electrical components are fabricated using integrated circuit processes, while the mechanical components are fabricated using micromachining processes that are compatible with the integrated circuit processes.
MEMS devices are found in an increasing number of applications, from sensor technology, to biomedicine, to telecommunications. Presently, some of the most interesting applications for MEMS devices are optical applications, wherein the tiny mechanical components include mirrors, prisms and/or gratings. For example, in the area of telecommunications, optical MEMS devices form optical switches, modulators, attenuators, and filters.
In most MEMS devices, one or more actuators are provided to position the tiny mechanical components. Some examples of MEMS actuators include electrostatic, thermal, electromagnetic, and/or piezoelectric actuators. In order to limit the actuation power, current, or voltage, and thus minimize the size and cost of the MEMS device, MEMS structures are generally designed to require a relatively low actuation energy. For example, when the mechanical components are coupled to the substrate via a cantilever or one or more springs, it is generally preferred that the spring constant(s) be relatively weak. However, MEMS structures with weak spring constants are susceptible to undesired perturbations. For example, mechanical shock or vibration often results in an impulse that occurs at the natural mechanical vibrational frequency of the MEMS structure.
If the MEMS structure is an integral part of a closed loop control system, which is subject to this impulse error, the control system will apply feedback in an attempt to neutralize the error. Unfortunately, most control systems operate at bandwidths much lower in frequency than the natural mechanical frequency of the MEMS structure in order to avoid difficulties associated with lag due to mechanical inertia. Accordingly, as the mechanical impulse damps out, the control system applies a delayed response to compensate. This compensation is not required, and thus introduces a large additional error due to inappropriate delayed feedback. This additional and delayed error significantly contributes to the operational shock sensitivity of MEMS devices.
It is an object of the instant invention to reduce the operational shock sensitivity of MEMS devices.